Completing oil wells



July 31, 1956 F. H. DEILY COMPLETING OIL WELLS Filed Dec. 14, 1954 OUTER PACKER INNER PACKER P- i CHECII(9VALVE/1 CABLE TO SURFACE TUBING CASING 8 i SINKER BAR F RACTURE FORK F RANCQBLE DISC ACCESS PORT 3O PE RF OIISATIONS E VACUATE D CHAMBER Fredric H. Deily Byw Attorney Invenfor stances completed using the following steps.

2,756,828 COMPLETING oIL WELLS Fredric H. Deily, Tulsa, Okla, assignor to Esso Research and Engineering Company, a corporation of Delaware Application December 14, 1954, Serial No. 475,229

'1 Claim. (Cl. 166-164) The present invention is broadly concerned with improved means for completing oil wells. More specifically it concerns a method and apparatus for removing materials from the surface of a subterranean oil reservoir where the reservoir is pierced by a drilled well. The invention further concerns an apparatus and method for inducing and increasing the flow of oil from an oil reservoir formation into a well. The invention especially relates to a method and apparatus for removing plugging materials from the perforations that are formed within an oil well by the use of devices such as perforating guns and shaped charges. The invention also especially relates to a method and apparatus for cleaning the interface between a formation and a well that pierces the formation.

When a drilling operation has successfully pierced a subterranean oil reservoir and it is desired to bring the formation into production, the oil well is in many in- First, a string of casing is lowered into the well and is cemented in position by forcing cement between the outer surface of the casing and the inner surface of the bore hole.

Then a perforating gun or shaped charges are lowered through a string of tubing into the well and down to the level of the reservoir formation. Here the gun or shaped charges are fired with the result that projectiles and/or hot gases are driven through the casing and cement to form a plurality of perforating channels within the reservoir formation. The perforations thereby provide small passageways directly within the formation which permit or facilitate the flow of oil from the formation into the well.

Even though a reservoir formation is perforated in the manner just described, a satisfactory flow of oil from the formation may be difficult to obtain. In the first place the entire surface area of the formation that lies immediately adjacent the well itself may be plugged with water or drilling mud as a result of the drilling operation. Second, the perforations themselves may be substantially plugged with finely divided material as a result of the explosions and they may also be filled with drilling mud or water. The net result of these factors as well as other factors is that the flow of oil from the reservoir formation into the well may be very small or even non-existent.

In an effort to clear a reservoir formation of the obstructions described above, a number of procedures are conventionally used in the petroleum producing industry. A first procedure consists in injecting acids or other fluid reagents into the well in order to chemically treat the interior surface of the reservoir formation. Some chemical treatments of this type are reasonably successful in inducing and increasing the flow of oil from the reservoir formation. A second procedure consists in the use of swabs which are lowered into the well through a string of tubing. These devices are essentially plungers provided with a one-way valve which opens when the swab is lowered through the tubing and closes when the swab tates Patent 2,756,828 Patented July 31, 1956 is raised in the tubing. Inasmuch as the swab is adapted to fit snugly against the interior wall of the tubing it is apparent that itacts much the same as a plunger pump and lifts the liquid within the tubing when it is moved up and down within the tubing. This action tends to lower the pressure differential between the reservoir and the wella factor which is more favorable toward the flow of oil in that direction.

The use of the aforementioned chemicals and swabs for inducing flow from a reservoir formation results in certain drawbacks and disadvantages that are well known to persons skilled in the art. Chemicals are generally expensive and present numerous handling problems that make them undesirable for general use. Swabs on the other hand are also relatively difficult to employ and furthermore provide pressure differentials of relatively low magnitude with the result that they are not always influential or effective in removing obstructions and the like from plugged formations.

In view of these shortcomings of the existing procedures, it is therefore an object of the present invention to provide an improved apparatus and method for unplugging subterranean oil reservoirs and for increasing the flow rate of oil from the reservoirs into adjacent oil wells. It is a particular object of the invention to provide means for cleaning out the perforations that are formed in such reservoirs by the use of devices such as perforating guns and shaped charges. These and other objectives will become more apparent with the description which follows.

In accordance with a process embodiment of the present invention the aforementioned objectives are realized by first sealing off a portion of an oil well that lies laterally adjacent a reservoir formation. An enclosed low pressure gas filled zone is then provided within the well at a point below the sealed portion and is separated from the portion by suitable quick opening means. The volume of the latter zone should be at least about equal to the volume of the sealed-off well portion and preferably between one and two times the volume of the sealed-off portion. The sealed-off portion is permitted to fill up with well fluid which may include drilling mud as well as fluid from within the formation; and at the desired moment the closed connection between the sealed off portion and the low pressure gas-filled zone is quickly opened whereby liquid from within the sealed off portion drops into the low pressure zone and thereby creates a pressure differential between the fluids within the reservoir formation and the pressure within the sealed off portion. The pressure within the sealed off portion of. the well is thereby reduced to substantially the same pressure as existed in the evacuated or gas filled zone immediately prior to the time when the two volumes were connected with one another. The sudden reduction to this pressure level from the pressure that originally existed in this portion of the well is contemplated to be suflicient and sudden enough to remove flow obstructions from the surrounding oil reservoir formation and to induce and promote the flow of oil from the formation into the well. When this condition has been realized, further completion of the well may be carried out in a conventional manner.

In a preferred process embodiment of the invention the gas filled zone is initially maintained at as high a vacuum as possible, thereby ensuring the greatest possible pressure differential between this zone and the oil reservoir formation. Furthermore, the quick opening procedure for providing fluid flow between the sealed off portion of the well and the low pressure gas chamber preferably consists of fracturing a frangible disc which ordinarily separates the two zones. Fracturing of this member may be realized by dropping a sinker bar or other weight down the well and impinging it upon an impact rod which in turn is adapted to strike upon and break the frangible member.

The process embodiment of the invention may be even better understood by reference to the accompanying figure which illustrates an apparatus embodiment of the invention which is contemplated to constitute the best means for carrying out the objectives of the invention. Referring to the figure, there may be seen an oil reservoir formation which constitutes one layer in the general lithologic pattern designated by the numeral 6. Also illustrated in the figure is a well 7 which pierces the reservoir formation 5. This well as illustrated has been cased as by means of casing 8 which in turn has been set and positioned within the well by means of cement 9.

In discussing the apparatus in the figure, it will be assumed that the well is filled with drilling mud or completion fluid and that the reservoir formation has been perforated as by means of a perforating gun or shaped charges of an explosive. The perforations formed by the gun or shaped charges are designated by the numeral 10. It will be seen that these perforations extend through the casing as well as the cement and form small passageways that penetrate well into the reservoir formation.

It will further be assumed that it is presently desired to induce or promote the flow of oil from the reservoir formation into the well proper. And finally it is assumed that this desired flow is obstructed by solid particles, mud and the like which have been deposited in the perforations by the projectiles from the perforating gun or by the gases from the shaped charges.

Having just described the situation which generally confronts production personnel when they have completed perforating a well, attention is now directed toward the apparatus which is illustrated in the figure and which is contemplated to constitute a preferred embodiment of the present invention. This apparatus consists of a substantially cylindrical hollow member 11 which is divided longitudinally into two separate zones 12 and 13. These two zones are separated by means of a frangible disc member 14 which is adapted to be fractured by an impact rod 15.

Both ends of the cylindrical member 11 are sealed as by means of end plates 16 and 17. The latter end plate which constitutes a portion of zone 12 is provided with a fluid passageway 18 and a one-way check valve 19 which is adapted to permit the flow of fluid from within zone 12 to a point outside of the zone. Fluid flow in the opposite direction is prevented by the action of the valve.

The outer diameter of cylindrical member 11 is smaller than the inner diameter of the casing 8 and is sealed thereto by means of suitable packers 20. These packers may be of any conventional type, as for example cup packers, inflatable packers and the like. The packers that are illustrated in the figure are of the cup type and are oriented so as to prevent the flow of fluid in either vertical direction within the annular space between the cylindrical member 11 and the casing 8.

The packers are arranged substantially at each vertical end of zone 12 so that the annular space between this zone and the casing 8 is sealed off from the remainder of the well. Zone 12 is also provided with ports 30 in its side walls so that fluid may readily flow from the annular space 21 into zone 12 and vice versa. Thus, fluid may flow from the formation 5 through the perforations into the annular space 21 and thence into zone 12, but flow in the opposite direction is substantially prevented by the check valve 19 in the passageway 18.

It should be further noted that member 11 may be introduced and supported within the well in any conventional manner. It is particularly contemplated that member 11 be secured to the bottom of a conventional tubing string 22 which extends from the top of the well down to the reservoir formation. Indeed, member 11 may actually constitute an integral part of such a tubing string.

Having described in detail the structural features of the apparatus in the figure, attention is now directed toward the manner in which the apparatus is operated. With the apparatus set as shown the frangible member 14 is fractured as by dropping a weight such as a sinker bar 23 down the tubing string and striking the top of the impact rod 15. Impact rod, upon being struck, in turn strikes the frangible disc, fractures the disc and causes liquid within zone 12 and the annular space to drop within the evacuated zone 13. Thus, the pressure within the annular space 21 and the zone 12 is substantially instantaneously dropped in value from the well or formation pressure in the vicinity of the reservoir formation down to whatever pressure existed in zone 13 prior to the fracture of the disc 14-. This decrease in pressure will be governed almost entirely by the depth of drilling mud in the well or the pressure of the formation 5, whichever is greater; and this decrease in pressure may range from 1000 to 5000 lbs. per square inch in most wells. The sudden decrease causes particles and occluded materials within the perforations 10 to be accelerated, dislodged and to fall within the annular space 21. Their removal from the reservoir formation plus the increased pressure differential between the formation and the sealed portion of the well thereby induces and promotes the flow of oil from the formation into the well.

If the flow of oil from the formation and the pressure of the formation are great enough, oil may actually flow through check valve 18 and up into the tubing string 22. It may be withdrawn from here to the top of the well in accordance with conventional procedures. Fluids in the tubing string, however, cannot flow back into the zone 12 because of the check valve 19, and the clearing of the perforations 10 is thus permanently realized.

It will be appreciated that the apparatus in the figure constitutes merely one example of the invention, and a number of modifications and variations may be employed without departing from the spirit or scope of the invention. For example, packers other than the proposed cuptype packers that are illustrated in the figure may be employed. Inflatable packers and the like may also be utilized.

On occasions it may be desirable to reduce the pressure within the chamber 12 and the annular space 21 before this chamber is suddenly vented into the evacuated chamber 13. Such a procedure, for example, is helpful in sealing the packers that are illustrated in the figure. Such a pressure reduction may be readily realized by merely lowering a swab within the tubing string 22 and swabbing the well for a short period of time suflicient to remove some of the liquid from zone 12 through check valve 19 and up into the tubing string 22.

It will also be noted that quick opening devices other than frangible disc 14 may be readily incorporated within the present apparatus. Thus, a number of quick opening valves and the like operated from the surface of the well may also be used.

The entire device may be a permanent installation as a part of the producing equipment. It may also be made wire line retrievable, so that it may be used on difierent well installations.

In summary, then, the present invention comprises a method and apparatus for cleaning the interfacial surface that exists between a subterranean formation and a well or hole that penetrates the formation. The invention achieves this objective by substantially instantaneously creating a large pressure drop across the interface that drives solid particles, drilling mud and other flowobstructing materials from the formation into the well or hole. The invention has particular application as a method and apparatus for cleaning out perforations that are formed by perforating guns, shaped charges, etc.

What is claimed is:

An apparatus for removing plugging material from the perforations in a perforated well which comprises a cylindrical body member adapted to be secured to the lower end of a tubing string, said body member being longitudinally divided into an upper liquid-filled zone and a lower gas-filled zone, quick opening means separating said zones in a fluid tight relationship, sealing means adapted to seal the annular space between the upper zone of said member and the inner surface of the well from the remaining well volume, combination conduit and check valve means adapted to provide flow of liquid from within said upper zone to the interior of said tubing string, ports in the side wall of said upper zone providing fluid access between said upper zone and said sealed-off annular space, and means for opening said quick opening means from the earths surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,098,520 Santiago Nov. 9, 1937 2,133,383 Erwin et a1 Oct. 18, 1938 2,138,375 Grant Nov. 29, 1938 2,361,558 Mason Oct. 31, 1944 2,659,442 Sutlifi Nov. 17, 1953 

